Sterilizing and packaging process utilizing gas plasma

ABSTRACT

A continuous flow of gas plasma is admitted to a substantially evacuated sterilization chamber containing the object to be sterilized. Argon plasma is produced continually by being subjected to a radio frequency field. Complex shapes such as capillary passages through a blood oxygenator can be sterilized by passing the gas plasma through them. The exterior of objects to be sterilized can be subjected to gas plasma within a packaging envelope, and subsequent to sterilization such envelope can be evacuated and collapsed onto the object to preserve its sterile character.

Fraser et al.

[ Dec. 3, 1974 STERILIZING AND PACKAGING PROCESS 3,323,163 5/1968Menashi....- 21/54 R UTILIZING GAS PLASMA 3,516,223 6/l970 Andersen etal. 53/112 B 3,600,126 8/1971 Hcllund 2l/l02 R Inventors: Sheila .1.Fraser, Sea Roger 3,705,652 12 1972 Russman 23/25 8.5

Gillette, Auburn; Richard L. Olson, Benevue an of wash- PrimaryExaminerM0rris O. Wolk [73] Assignee: The Boeing Company, Seattle,Assistant Examiner T- Hagan Wash. Attorney, Agent, or Firm-Robert W.Beach [22] Filed: Dec. 13, 1971 [57] ABSTRACT [21'] Appl' 207487 Acontinuous flow of gas plasma is admitted to a substantially evacuatedsterilization chamber containing 52] us. (:1. 53/21 FC, 21/54 R, 21/102,the Object to be sterilized. Argon plasma is Produced 53 3 25 5continually by being subjected to a-radio frequency 51 1m. (:1 B65b31/02, B65b 55/12 fibld- Complex Shapes Such as Capillary P g [58] Fieldat Search 21/54, 102; 53/22, 111 R, through a blood bxygenatbr can besterilized y p 53 1 A, 111 B 111 RC 112 R, 112 A, 112 ing the gas plasmathrough them. The exterior of ob- B 21 3 3 3 5 jects to be sterilizedcan be subjected to gas plasma 20 32 R; 250/531 within a packagingenvelope, and subsequent to sterilization such. envelope can beevacuated and collapsed 56] References Cited onto the object to preserveits sterile character. UNITED STATES PATENTS 6 Claims, 4 Drawing Figures2,972,349 -2/l96l DeWall 23/2585 "Zak/METER E I .coou/va 6 (EM Eaint/2,4770 CHANEL-E /Z DIFFUSION? MfC/M/Y/CAL VACUUM PUMPS EE MATCH/N6FF g NETWORK V41 V15 GE/VEEA 7'0 I 5 (7 3 2 f FUWEE METEIZ "9 1STERILIZING AND PACKAGING PROCESS UTILIZING GAS PLASMA This inventionrelates to the sterilization by the use of coal gas plasma of articlessufficiently fragile so that they cannot be subjected to a high pressuredifferential or which are made of material that will become plasticormelt at high temperatures, or which would be damaged if subjected tothermal shock by an abrupt temperature change.

A principal object of the present invention is to provide a sterilizingand packaging process in which the sterilizing effectiveness of gasplasma is increased by providing a continued flow of the gas plasma oversurfaces to be sterilized with minimum dilution by air.

Another object is to cover immediately surfaces which have beensterilized by flow of gas plasma over them so as to preserve theirsterile character.

F IG. 1 is adiagram of representative sterilizing apparatus utilizinggas plasma according to the present invention. l I

1316' 2. s a. dia ta of anqt zqnm of s ih i t apization chamber 1.

paratususing the plasma process of the present invention, parts beingshown in section. FIG. 3 and FIG. 4 are detail elevations of somewhatmodified portions of the apparatus shown in-FIG. 2. i

Sterilization of articles by the process of the present invention isaccomplished in a sterilization chamber 1. An article 2 to besterilizedis inserted into such chamber through a suitable aperture closable towithstand substantial external pressure. Preferably the chamber isprovided in a metal casing of cylindrical shape which can be evacuatedwithout collapsing.

Gas such as argon from-which the gas plasma is produced is supplied froma tank 3-in which it is stored under pressure through a'flowmeter' 4tothe plasma production conduit 5 connected to one end of thesterilization chamber 1. Such 'plasma produ ction conduit is subjected'to a radio-frequency field created by the electrodes 6, whi chmay'encircle such conduit. A suitable radio-frequency generator 7-is'connected to the electrodes '6 through an impedance matching network 8for coupling the ,capacitativeelectrodes 6 to an amplifier of theradio-frequency generator 7. The oscillator and amplifier of theradio-frequency generator should be capable of producing up to'3'00watts of continuous power'as indicated by the power meter 9.

It may be desirable to cool the plasma generator conduit 5 by passingcooling water through the cooling jacket 10. The supply of gas to theplasma generator can be regulated by a valve 11 as wellas automaticallyby the flowmeter 4; and the flowmeter pressure gauge 12 will indicatethe amount of gas supplied to the plasma-generating tube 5. 3 r

The quantity of gasplasma flowing through the'sterilization chamber 1 isdetermined, not only by the flow meter 4 and the valve 11, but also bythe pressure in the sterilization chamber 1 through which the plasmaflows. The pressure in such sterilization chamber is preferably quitelow, not exceeding a few millimeters of mercury. The pressure in'thesterilization chamber could'be indicatedby a pressure gauge 14.

The supply of gas to the plasma generator from the tank 3 can becontrolled by a shutoff valve 15. When it is desired to use theapparatus, the article to be sterilized is placed in the sterilizationchamber l, the vacuum pump 13 is started to evacuate the chamber; andthe shut-off valve 15 is openedto enable gas'to flow The radio-frequencygenerator 7 is then energized and the impedance matching network 8 isadjusted to minimize reflected power. The article is subjected to theflow over it of the gas plasma passing through the sterilization chamberfor the period of time required to effect sterilization. Reductions inmicrobial population as much as 99% have been accomplished by exposureof the article .to be sterilized to plasma flowfor a period of time asshort as five minutes.

When the sterilization of the particular article has been completed, theradio frequency generator 7 is deenergized, the gas supply valve I5 isclosed, and the vacuum pump 13 is stopped or its connection to thesterilization chamber is severed by a suitable valve. The sterilizationchamber is then vented to atmosphere, the chamber is opened, and thesterilized object removed from it.

The apparatus shown in FIGS. 2, 3 and 4 is of the type particularlyadapted to the sterilization of artificial lung blood oxygenators. Theapparatus preferably is capable of sterilizing several of suchoxygenators at the same time, three of such oxygenators, 2a, 2b and 2c,being shown in FIG. 2. Such oxygenators are housed in the sterilizationchamber 1 during the sterilization operation. Thev apparatus shown inFIG. 2 includes components generally similar to those described inconnection with the apparatus of FIG. 1. v

Gas to be excited into plasma is'supplied from the supplying tank 3through the flowmeter ,4,-to a' manifold 5' of the plasma generator.-The amount of gas flow is indicated by the flowmeter pressure gauge 12and the flow to the sterilization chamber'canbe' initiated andterminated by operation of the shutoffvalve 15. Flow of the gas plasmathrough the sterilization chamber 1' is induced by suction created bythe vacuum pump 13. Theconnection between the sterilization chamber andthe vacuum pump can be severed by closing valve 16 to avoid thenecessity of stopping thevacuum pump between sterilizing operations. Anoil trap I'Zmay be included in the suction line to pump 13, an'd aventing valve l8 for connecting the sterilization chamber 1' withatmosphere may be provided in the suction line to the vacuum pump. I

Individual pipes 5'f connect the manifold 5 to the individualoxygenators 2a, 2b and 2c, respectively-A radio frequency field. forconverting the gas to plasma is produced by the exciters 6 in each ofthe gassupply pipes 5". The radio-frequency field is created by suchexciters connected'to the radio-frequency generator 7, including anoscillator and an amplifier. The impedance matching network is adjustedby the radiofrequency tuner'8, and the power ,of the radio frequencyoscillator is indicated by the wattmeter 9'.

The blood oxygenators to be sterilized are shown in oxygenator includesa multiplicity of capillary tubes 22 through which the gas plasma flowsslowly to effect the sterilizing action. The resistance to flow of gasplasma through different oxygenators may vary, and the opening of valves19 can be adjusted to equalize the flow effected through the oxygenatorsfrom the common manifold Although it is only essential that theinteriors of the capillary passages through the oxygenator be sterilebecause only such capillary passages come into contact with blood beingoxygenated, it is desirable to have a completely sterilized oxygenatorpackaged in a sealed container to facilitate storage. It is thereforedesirable to provide for flow of gas plasma over the exterior of theoxygenator at the same time that gas plasma is flowing through thecapillary passages of the oxygenator.

FIG. 3 shows an enclosure 23 for the oxygenator having an inlet 24 andan outlet 25 for flow of gas plasma between the enclosure and theexterior of the oxygenator to the interior of the sterilization chamber1' shown in FIG. 2. Such enclosure is sealed around the inlet 20 and theexit 21 for the gas plasma flowing through the interior of theoxygenator. If the enclosure is in the form of a plastic bag, theopenings 20, 21, 24 and 25 can all be sealed to maintain the sterilizedcondition both of the interior and of the exterior of the oxygenator.

In the construction shown in FIG. 4 the gas plasma flows through theinterior of the oxygenator 2' and then over the exterior of theoxygenator sequentially. In this instance the plasma exit 21 from theinterior of the oxygenator discharges into the interior of the enclosure23. The gas plasma is then discharged from the interior of suchenclosure, after passing over the exterior of the oxygenator, throughthe exit 25' to the interior of the sterilization chamber 1' shown inFIG. 2. With the use of such an arrangement it is necessary to closeonly the inlet passage 20 leading to the interior of the oxygenator, andthe exit 25' leading from the enclosure 23.

By providing continual flow of the gas plasma through the apparatus andover the surfaces of the arti-' cle to be sterilized, the sterilizingoperation is effected in a more efficient and expeditious manner. Thesterilizing action of the gas plasma is also rendered more effective andconsequently more expeditious by exposing the surfaces tobe sterilizedin a low pressure atmosphere, so that the gas plasma is more dense. Thegas plasma can be formed from various gases, but preferably is derivedfrom a monatomic inert gas such as argon, helium or xenon. Such a gasmay be excited to form gas plasma by utilizing known techniques such asby subjecting it to a radio-frequency field as discussed above, by atechnique such as described in the articles Analytical Applications ofElectrodelessly Discharged Gases and Research With ElectrodelesslyDischarged Gases published in the periodical Journal of ChemicalEducation, Volume 43, Number 5, May. 1966 and Number 6, June, 1966,respectively.

While the specific application of the sterilization process describedabove with respect to FIGS. 2, 3 and 4 relates to the sterilization ofoxygenators, the process is particularly advantageous for thesterilization of various kinds of medical and hospital equipment.Another important application of the process is for sterilization ofexcrement or other waste material which must be stored for a time, suchas in an airplane or a spacecraft, before being discarded. Such wastematerial may be ejected from a spacecraft and should be sterilizedbefore ejection.

We claim:

1. The process of sterilizing an article which comprises'enclosing thearticle in a container, enclosing the container in a sealable chamber,maintaining subatmosphere pressure in the chamber and in the container,and, while maintaining such subatmosphere pressure in the chamber and inthe container, flowing nonoxidizing gas plasma into the container, overa surface of the article to be sterilized and then out of the containerinto the portion of the chamber exteriorly of the container, terminatingsuch flow of gas plasma through the container, and sealing the containerto form a sterilized package for the article.

2. The process defined in claim 1, in which the container is a plasticbag having sealable openings.

3. The process defined in claim 1, in which the flow of gas plasma ispassed sequentially over the interior and exterior surfaces of thearticle.

4. The process defined in claim 3, in which the article is a bloodoxygenator having a plurality of capillary passages therethrough and aflow of nonoxidizing gas plasma is passed through the capillarypassages.

5. The process defined in claim 1, in which the article is a bloodoxygenator having a plurality of capillary passages therethrough and aflow of nonoxidizing gas plasma is passed through the capillarypassages.

6. The process defined in claim 5, in which the container is a plasticbag having an opening, the oxygenator has a tube extending through theopening of the plastic bag and communicating with the interior of theoxygenator, and such bag opening and tube are sealable after the flow ofnonoxidizing gas plasma through the bag opening and the tube has beenterminated.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,851,436December 3, 1974 Inventor(s) Shelia J. Fraser, Roger B. Gillette andRichard L. Olson It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 4, cancel "coal" and insert cool-n En'gned and Scaledthis Twentieth Day of February 1979 [SEAL] Attestn A ,B RUTH c. MASON WW ER Attesting Oflicer Commissioner of Patents and Trademarks

1. The process of sterilizing an article which comprises enclosing thearticle in a container, enclosing the container in a sealable chamber,maintaining subatmosphere pressure in the chamber and in the container,and, while maintaining such subatmosphere pressure in the chamber and inthe container, flowing nonoxidizing gas plasma into the container, overa surface of the article to be sterilized and then out of the containerinto the portion of the chamber exteriorly of the container, terminatingsuch flow of gas plasma through the container, and sealing the containerto form a sterilized package for the article.
 2. The process defined inclaim 1, in which the container is a plastic bag having sealableopenings.
 3. The process defined in claim 1, in which the flow of gasplasma is passed sequentially over the interior and exterior surfaces ofthe article.
 4. The process defined in claim 3, in which the article isa blood oxygenator having a plurality of capillary passages therethroughand a flow of nonoxidizing gas plasma is passed through the capillarypassages.
 5. The process defined in claim 1, in which the article is ablood oxygenator having a plurality of capillary passages therethroughand a flow of nonoxidizing gas plasma is passed through the capillarypassages.
 6. The process defined in claim 5, in which the container is aplastic bag having an opening, the oxygenator has a tube extendingthrough the opening of the plastic bag and communicating with theinterior of the oxygenator, and such bag opening and tube are sealableafter the flow of nonoxidizing gas plasma through the bag opening andthe tube has been terminated.